The present invention relates generally to improvements in portable combustion powered fastener driving tools, particularly to improvements relating to the suspension of a motor for a combustion chamber fan for decreasing the operationally-induced axial acceleration and oscillation of the motor to decrease wear and tear on the motor, and specifically in applications where low-cost, iron core fan motors are employed to power the combustion chamber fan motor.
Portable combustion powered, or so-called IMPULSE(copyright) brand tools for use in driving fasteners into workpieces are described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722, 5,197,646 and 5,263,439, all of which are incorporated by reference herein. Similar combustion powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE(copyright) brand.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces the spark for ignition, and a fan located in the combustion chamber provides for both an efficient combustion within the chamber, and facilitates scavenging, including the exhaust of combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the ignition of a charge of gas in the combustion chamber of the engine, the piston and driver blade are shot downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or xe2x80x9creadyxe2x80x9d position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Upon ignition of the combustible fuel/air mixture, the combustion in the chamber causes the acceleration of the piston/driver blade assembly and the penetration of the fastener into the workpiece if the fastener is present. This combined downward movement causes a reactive force or recoil of the tool body. Hence, the fan motor, which is suspended in the tool body, is subjected to an acceleration opposite the power stroke of the piston/driver blade and fastener.
Then, within milliseconds, the momentum of the piston/driver blade assembly is stopped by the bumper at the opposite end of the cylinder and the tool body is accelerated toward the workpiece. Therefore, the motor and shaft are subjected to an acceleration force which is opposite the direction of the first acceleration. These reciprocal accelerations cause the motor to oscillate with respect to the tool. The magnitude of the accelerations, if left unmanaged, are detrimental to the life and reliability of the motor.
Conventional combustion powered tools of the IMPULSE(copyright) type require specially designed motors to withstand these reciprocal accelerations of the shaft and motor, and the resulting motor oscillations. Among other things, the motors are preferably of the ironless core type, and are equipped with internal shock absorbing bushings, thrust and wear surfaces, and overall heavier duty construction. Such custom modifications result in relatively expensive motors which increase the production cost of the tools.
Thus, there is a need for a motor suspension mechanism for a combustion powered tool which reduces operating demands on the motor, increases reliability of the motor, and allows the use of closer to standard production fan motors to reduce the tool""s production cost. In an ongoing attempt to reduce manufacturing costs, it is desirable to use the lowest cost fan motor possible for this application. At this time, such a motor is a conventional iron core motor, also known as permanent magnet, brushed DC motor of the type produced by Canon and Nidec Copal of Japan, as well as many other known motor manufacturers. When iron core motors were employed as combustion tool fan motors, the conventional suspension was found to result in an underdampened condition, wherein the motor oscillated excessively and out of tune relative to the operational oscillation of the combustion tool, as described above. In other words, there is a mechanical impedance mismatch between the combustion tool and the combustion chamber fan motor. This is due in large part to the greatly reduced weight of the iron core motors as compared to conventional motors. The iron core motors weigh only about ⅓ as much as conventional ironless core combustion chamber fan motors. The iron core motors are less durable, and are incapable of withstanding the degree of 50 g forces or higher which are generated through combustion.
As a result, in operation, the conventional combustion tool motor suspensions underdampen the iron core motor. This underdampening significantly reduces the effectiveness of the suspension, and subjects the motor to damaging axial forces. Instead, the goal is to achieve critical dampening, in which there is just enough dampening to receive the combustion-generated motion and prevent oscillation past equilibrium.
One way to achieve critical dampening between the fan motor and the combustion tool is to increase its flexibility, as by reducing the mass of the resilient suspension member which circumscribes and projects radially from the motor and the motor container to fasten those components to the combustion head of the tool. It has been found that increasing the flexibility in this way, to a degree which will satisfactorily suspend the iron core motor, also results in the unsatisfactory situation wherein the suspension member loses its resiliency and, upon the generation of the forces initiated by combustion, is unable to return the motor to the designated start position.
Another design parameter of combustion tools is that, while capacitors are known for reducing voltage spikes and transients for brushed motors, and it is advantageous to place the capacitor closer to the source of the spikes and transients, capacitors were not able to survive the impact forces generated in a combustion tool at the fan motor. Thus, such noise suppression capacitors had to be mounted in more remote, and less effective locations on the tool.
Thus, there is a need for a combustion tool fan motor suspension which can accommodate an iron core motor and provide sufficient dampening to protect the motor from combustion-generated impact forces. There is also a need for a combustion tool fan motor suspension which allows the mounting of a noise suppression capacitor on or near the fan motor.
Accordingly, it is an object of the present invention to provide an improved combustion powered tool with an improved suspension mechanism for an iron core combustion chamber fan motor, in which the suspension reduces operationally-induced reciprocal accelerations of the motor while keeping the oscillations of the motor within an acceptable range.
Another object of the present invention is to provide an improved combustion powered tool which features a mechanism for dampening operationally-induced oscillation of the combustion chamber fan motor, especially when the motor is of the iron core type.
It is a further object of the present invention to provide an improved combustion powered tool having a suspension which is mounted to the tool to xe2x80x9cfloatxe2x80x9d relative to the combustion chamber and thus dampen combustion induced vibrations.
It is yet another object of the present invention to provide an improved combustion powered tool having a suspension mechanism for a combustion chamber fan motor which increases the life of the motor.
It is still another object of the present invention to provide an improved combustion powered tool having a suspension mechanism for a combustion chamber fan motor which can accommodate the mounting of a noise suppression capacitor on or near the fan motor.
The above-listed objects are met or exceeded by the present improved combustion powered fastener tool, which features a mechanism for suspending a combustion chamber fan motor that reduces the effects of the reciprocal axial acceleration of the motor, and the resulting oscillation of the motor, during operation of the tool. In the preferred embodiment, the assembly includes a flexible rubber web vulcanized to a motor retaining ring. The web is also vulcanized to a cylinder head mounting bracket so that only the web secures the ring to the bracket. In addition, the bracket is mounted via threaded fasteners and bushings to the cylinder head so that it will xe2x80x9cfloatxe2x80x9d relative to the movement of the combustion chamber. To this end, the bracket features resilient standoffs located at the cylinder head mounting points which provide progressive dampening. As the motor changes position, dampening increases. As such, the present motor suspension mechanism provides more accurately tuned dampening to iron core fan motors than conventional suspensions. Another feature of the present motor suspension is that it permits the mounting of a noise suppression capacitor on the fan motor.
More specifically, the present invention provides a suspension mechanism for a motor of a combustion chamber fan in a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece, the tool generating an upward axial acceleration of the motor upon combustion in the chamber, a subsequent reciprocal axial acceleration of the motor when the piston bottoms out on a bumper, at least one of the accelerations causing the motor to oscillate relative to the tool, the suspension mechanism includes a suspending portion configured for providing progressive dampening to the motor upon the generation of the axial accelerations.
In another embodiment, the present invention provides a suspension mechanism for a motor of a combustion chamber fan in a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece, the suspension mechanism comprising a motor mounting bracket which, upon fastening to a cylinder head of the tool, is configured to be movable relative to the cylinder head.
In yet another embodiment, the present invention provides a suspension mechanism for a motor of a combustion chamber fan in a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece, the suspension mechanism including a rigid motor retaining ring defining a cup for accepting the motor, the motor having an armature shaft end, said motor retaining ring being configured so that the motor is secured thereto only at the armature shaft end.
In addition, the present invention also provides a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece. The tool includes a combustion chamber defined in part by a cylinder head, a combustion chamber fan, a motor connected to said fan and a suspension mechanism for the motor configured for regulating the relative axial movement of the motor relative to the cylinder head. The suspension mechanism includes a suspending portion configured for providing progressive dampening to the motor upon the initiation of axial acceleration of the cylinder head.